Abstract

Identifying the energy minima of molecular clusters is a challenging problem. Traditionally, search algorithms such as simulated annealing, genetic algorithms, or basin hopping are usually used in conjunction with empirical force fields. We have implemented a basin hopping search algorithm combined with density functional theory to enable the optimization of molecular clusters without the need for empirical force fields. This approach can be applied to systems where empirical potentials are not available or may not be sufficiently accurate. We illustrate the effectiveness of the method with studies on water, methanol, and water + methanol clusters as well as protonated water and methanol clusters at the B3LYP+D/6-31+G* level of theory. A new lowest energy structure for H+(H2O)7 is predicted at the B3LYP+D/6-31+G* level. In all of the protonated mixed water and methanol clusters, we find that H+ prefers to combine with methanol rather than water in the lowest-energy structures.

Received 01 August 2012Accepted 17 September 2012Published online 03 October 2012

Acknowledgments:

We thank the University of Nottingham High Performance Computing facility for providing computer recourses and the Engineering and Physical Sciences Research Council (EPSRC) for funding (Grant No. EP/I012303). We are grateful to Professor Jonathan Hirst for useful comments on the paper.